During metal machining, energy is primarily consumed in the formation and movement of the chip being cut from the workpiece. As such, it should be appreciated that the primary concerns for the efficient and economical machining of a workpiece are related to the rate of chip removal and the length of the service life of the tool being employed. As the rate of chip removal or cutting increases, more heat is generated and the operating temperature of the cutting tool also increases. This increase in temperature may become sufficient to adversely effect the service life of the cutting tool. Accordingly, the overall efficiency of the machining operation is uniquely dependent upon the quick and effective removal of heat, particularly at the tool/chip interface.
In order to achieve effective heat removal, it has been recognized for many years to utilize cutting fluids that not only provide direct cooling but also lubrication for friction reduction and less heat generation. The rate of flow and the direction of application of the cutting fluid are important.
At present, the most common approach utilized to provide a coolant/lubricant to the cutting zone is to provide a flood of fluid directed over the back of the chip. In this manner, heat generated during the contact of the tool with the workpiece is extracted via the chip. Unfortunately, at higher speeds (e.g. over 400 sfpm), it has been shown that cutting fluids applied in this manner lose their effectiveness as coolants. This may be attributed to the greater rate of heat generation due to higher speed machining, the inability of the cutting fluid to reach the cutting tool/chip interface region to be cooled and/or the tendency for faster motion of the chip and workpiece to carry the fluid away from the cutting zone. Accordingly, it should be appreciated that the flood of fluid approach, now commonly practiced in the art, significantly limits machining speeds. Thus, if speed of machining is to be increased, a new approach needs to be developed.
A number of attempts have recently been made to achieve this end and improve cooling and lubrication to allow effective higher speed machining. In what is believed to be the most effective approach to date, a remote nozzle directs a waterjet pressurized up to 40,000 psi toward the tool/chip interface (see FIG. 1). This approach is disclosed in the article "Metal Machining with High-Pressure Water-Jet Cooling Assistance - A New Possibility", from the publication Journal of Engineering for Industry, Feb. 1989, volume 111, pages 7-12.
While this approach has achieved promising results, it still suffers from a number of drawbacks. Specifically, at still higher speeds of operation, a remote waterjet is simply not able to direct a stream with sufficient pressure and accuracy so as to fully penetrate into the interface formed between the cutting tool and the chip. Accordingly, this high heat zone does not receive sufficient cooling or lubrication and the rotary cutting tool temperature rises to a level that adversely effects service life. Cutting performance is also adversely affected. Specifically, it should be appreciated that as the rotary cutting tool undergoes wear, chip control by the tool is adversely affected. This serves to adversely effect dimensional accuracy and surface quality. Accordingly, a need is identified for an improved high speed machining apparatus and method.